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  • 1
    Language: English
    In: Journal of Hydrology, Jan 16, 2014, Vol.508, p.299(8)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jhydrol.2013.09.056 Byline: Jakob Schelker, Karin Ohman, Stefan Lofgren, Hjalmar Laudon Abstract: acents Final-felling increases DOC concentrations in downstream rivers. acents Concentration increases dependent on the percentage clear-cut area. acents Lakes and ponds may attenuate the downstream effects. acents Significant increases occur if more than 11-25% are final-felled. acents Threshold values could be used to minimize the negative effects. Article History: Received 31 May 2013; Revised 6 September 2013; Accepted 20 September 2013 Article Note: (miscellaneous) This manuscript was handled by Laurent Charlet, Editor-in-Chief, with the assistance of P.J. Depetris, Associate Editor
    Keywords: Ponds
    ISSN: 0022-1694
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Journal Of Geophysical Research-Space Physics, 2011, Vol.116
    Description: The mobilization of mercury and dissolved organic carbon (DOC) during snowmelt often accounts for a major fraction of the annual loads. We studied the role of hydrological connectivity of riparian wetlands and upland/wetland transition zones to surface waters on the mobilization of Hg and DOC in Fishing...
    Keywords: Environmental Sciences Related To Agriculture And Land-Use ; Miljö- Och Naturvårdsvetenskap
    ISSN: 0148-0227
    E-ISSN: 21562202
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  • 3
    Language: English
    In: Journal of Hydrology, 16 January 2014, Vol.508, pp.299-306
    Description: Forest clear-cutting has been found to significantly increase concentrations of dissolved organic carbon (DOC) in boreal first-order streams. Here, we address the questions of (1) how the additional inputs of DOC by upstream forest harvesting affect downstream locations within a stream network and (2) what catchment area has to be harvested to cause a significant downstream increase in DOC concentration. We combined the use of primary data from a paired-catchment experiment, clear-cut history of a nested stream network derived from satellite images with a mixing-model approach in order to quantify the importance of upstream clear-cuts on two downstream sites with different catchment sizes. Modeled [DOC] agreed well with the measured concentrations in the smaller, 8.7 km catchment located above a larger wetland area, but discrepancies occurred for the larger 22.9 km catchment located downstream of the wetland. Estimates of the critical area ( ) needed to be harvested to cause a significant impact on downstream DOC concentrations was quantified to be 11% for 〈 0.05 and 23–25% for 〈 0.001. Our results suggests that (i) increased DOC concentrations induced by forest harvesting affect downstream sites and (ii) additional DOC inputs by harvests have a significant impact on stream water quality, if harvests exceed . We suggest that the estimates of could be used in sensitive river networks to provide harvesting-thresholds. The latter could be implemented into forest planning that includes considerations of the negative impact of clear-cutting on water quality.
    Keywords: Boreal Forest ; Clear-Cutting ; Dissolved Organic Carbon ; Scaling ; Harvesting Threshold ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Source: ScienceDirect Journals (Elsevier)
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  • 4
    In: Limnology and Oceanography, March 2016, Vol.61(2), pp.558-571
    Description: Streams and rivers transport dissolved organic matter (DOM) from the terrestrial environment to downstream ecosystems. In light of climate and global change it is crucial to understand the temporal dynamics of DOM concentration and composition, and its export fluxes from headwaters to larger downstream ecosystems. We monitored DOM concentration and composition based on a diurnal sampling design for 3 years in an Alpine headwater stream. We found hydrologic variability to control DOM composition and the coupling of DOM dynamics in the streamwater and the hyporheic zone. High‐flow events increased DOM inputs from terrestrial sources (as indicated by the contributions of humic‐ and fulvic‐like fluorescence), while summer baseflow enhanced the autochthonous imprint of DOM. Diurnal and seasonal patterns of DOM composition were likely induced by biological processes linked to temperature and photosynthetic active radiation (PAR). Floods frequently interrupted diurnal and seasonal patterns of DOM, which led to a decoupling of streamwater and hyporheic water DOM composition and delivery of aromatic and humic‐like DOM to the streamwater. Accordingly, DOM export fluxes were largely of terrigenous origin as indicated by optical properties. Our study highlights the relevance of hydrologic and seasonal dynamics for the origin, composition and fluxes of DOM in an Alpine headwater stream.
    Keywords: Hydrodynamics – Observations ; Streamflow – Observations ; Alpine Ecosystems – Observations;
    ISSN: 0024-3590
    E-ISSN: 1939-5590
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  • 5
    In: Limnology and Oceanography, September 2016, Vol.61(5), pp.1826-1838
    Description: Surface waters contribute substantially to carbon dioxide (CO) emissions to the atmosphere. However, global estimates remain uncertain due to methodological difficulties, such as in precisely estimating gas transfer in steep upland streams. Here, we addressed the question of what drives CO evasion from steep mountainous stream network of the European Alps by assessing the spatial and temporal variation of partial pressure of CO (CO) for 148 streams and the gas transfer coefficient for CO () for 88 locations within this 254 km watershed. Results show that log can be predicted reasonably well ( = 0.71, 〈0.001,  = 88) using a statistical model based on slope, average width, flow velocity and stream discharge. Also, most sites were supersaturated in CO with significant variation in CO due to season (September vs. December) and time of day (day vs. night), but not stream order. Resulting median CO evasion rates were 145, 119, 46, 43, and 50 mg C m h at 1 to 5 order streams, respectively. CO evasion was dependent on season and time of day, with the highest evasion (184.0 kg C h) during growing season at nighttime, followed by 124.6 kg C h during daytime. Dormant season nighttime evasion was 30.9 kg C h and daytime evasion only 17.1 kg C h. Overall we conclude that CO evasion of steep mountainous streams depends on seasonal and diurnal variation in CO and reach‐specific variability in . These controls strongly alter landscape‐scale CO evasion estimates, with implications for regional to global carbon budgets.
    Keywords: Atmospheric Carbon Dioxide – Environmental Aspects ; Diurnal Cycles (Earth Sciences) – Observations;
    ISSN: 0024-3590
    E-ISSN: 1939-5590
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  • 6
    In: Limnology and Oceanography, May 2018, Vol.63(3), pp.1355-1371
    Description: Lakes are an inherent component of the global carbon cycle. They receive dissolved organic matter (DOM) from the catchment, which is stored, transformed and respired, or delivered downstream. In this study, we show that a subalpine lake shifts its role from DOM “transporter” to “transformer” depending on season and climate. We monitored dissolved organic carbon (DOC) concentration and DOM optical properties at the inlet and outlet of subalpine Lake Lunz (Austria) at high frequency during two contrasting years: an extreme drought in 2015, and regular precipitation regime in 2016. During both years, the DOC mass balance revealed that inflowing and outflowing DOC loads were nearly balanced (+6.57% and +1.70% DOC production in 2015 and 2016, respectively). However, DOM optical properties revealed an in‐lake turnover of DOM compounds, so that the terrestrial and aromatic signature of inflowing DOM was modified into autochthonous, protein‐like DOM. The magnitude of this transformation varied seasonally, being maximal in summer and minimal in winter, presumably following periods of high and low primary production and photo‐degradation. Inter‐annually, we found that drought further increased DOM transformation during summer by extending the lake water residence time. Finally, our results demonstrate a rapid response of DOM dynamics to hydrological and meteorological changes at both seasonal and inter‐annual scales, suggesting that carbon cycling in clear‐water mountain lakes may be highly sensitive to hydrological variation.
    ISSN: 0024-3590
    ISSN: Limnology and Oceanography
    E-ISSN: 1939-5590
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  • 7
    Language: English
    In: 2013
    Description: Dissolved organic carbon (DOC) is a fundamental variable defining boreal stream ecosystems. In this thesis the impact of forestry practices that are commonly performed in the boreal regions of Scandinavia for stream water quality were evaluated. The thesis is based on combining the use of primary data...
    Keywords: Geosciences, Multidisciplinary ; Multidisciplinär Geovetenskap ; Oceanography, Hydrology, Water Resources ; Oceanografi, Hydrologi, Vattenresurser ; Environmental Sciences ; Miljövetenskap ; Forest Science ; Skogsvetenskap ; Soil Science ; Markvetenskap
    Source: SwePub (National Library of Sweden)
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  • 8
    Language: English
    In: Biogeochemistry, 2013, Vol.113(1), pp.451-466
    Description: The Adirondack region of New York has been identified as a hot spot where high methylmercury concentrations are found in surface waters and biota, yet mercury (Hg) concentrations vary widely in this region. We collected stream and groundwater samples for Hg and organic carbon analyses across the upper Hudson River, a 493 km 2 basin in the central Adirondacks to evaluate and model the sources of variation in filtered total Hg (FTHg) concentrations. Variability in FTHg concentrations during the growing seasons (May–Oct) of 2007–2009 in Fishing Brook, a 66-km 2 sub-basin, was better explained by specific ultra-violet absorbance at 254 nm (SUVA 254 ), a measure of organic carbon aromaticity, than by dissolved organic carbon (DOC) concentrations, a commonly used Hg indicator. SUVA 254 was a stronger predictor of FTHg concentrations during the growing season than during the dormant season. Multiple linear regression models that included SUVA 254 values and DOC concentrations could explain 75 % of the variation in FTHg concentrations on an annual basis and 84 % during the growing season. A multiple linear regression landscape modeling approach applied to 27 synoptic sites across the upper Hudson basin found that higher SUVA 254 values are associated with gentler slopes, and greater riparian area, and lower SUVA 254 values are associated with an increasing influence of open water. We hypothesize that the strong Hg–SUVA 254 relation in this basin reflects distinct patterns of FTHg and SUVA 254 that are characteristic of source areas that control the mobilization of Hg to surface waters, and that the seasonal influence of these source areas varies in this heterogeneous basin landscape.
    Keywords: Mercury ; Dissolved organic carbon ; Aromatic ; SUVA ; Adirondack
    ISSN: 0168-2563
    E-ISSN: 1573-515X
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  • 9
    Language: English
    In: Sci Rep, 2017, Vol.7(1), pp.14401-14401
    Description: Streams are significant sources of CO to the atmosphere. Estimates of CO evasion fluxes (f ) from streams typically relate to the free flowing water but exclude geomorphological structures within the stream corridor. We found that gravel bars (GBs) are important sources of CO to the atmosphere, with on average more than twice as high f as those from the streamwater, affecting f at the level of entire headwater networks. Vertical temperature gradients resulting from the interplay between advective heat transfer and mixing with groundwater within GBs explained the observed variation in f from the GBs reasonably well. We propose that increased temperatures and their gradients within GBs exposed to solar radiation stimulate heterotrophic metabolism therein and facilitate the venting of CO from external sources (e.g. downwelling streamwater, groundwater) within GBs. Our study shows that GB f increased f from stream corridors by [median, (95% confidence interval)] 16.69%, (15.85–18.49%); 30.44%, (30.40–34.68%) and 2.92%, (2.90–3.0%), for 3, 4 and 5 order streams, respectively. These findings shed new light on regional estimates of f from streams, and are relevant given that streamwater thermal regimes change owing to global warming and human alteration of stream corridors.
    Keywords: Biology;
    ISSN: 2045-2322
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  • 10
    Language: English
    In: Environmental science & technology, 07 July 2015, Vol.49(13), pp.7851-9
    Description: The complexity of mercury (Hg) biogeochemistry has made it difficult to model surface water concentrations of both total Hg (THg) and especially methylmercury (MeHg), the species of Hg having the highest potential for bioaccumulation. To simulate THg and MeHg variation in low-order streams, we have adapted a conceptual modeling framework where a continuum of lateral flows through riparian soils determines streamflow concentrations. The model was applied to seven forest catchments located in two boreal regions in Sweden spanning a range of climatic, soil, and forest management conditions. Discharge, and simulated riparian soil water concentrations profiles, represented by two calibrated parameters, were able to explain much of the variability of THg and MeHg concentrations in the streams issuing from the catchments (Nash Sutcliffe (NS) up to 0.54 for THg and 0.58 for MeHg). Model performance for all catchments was improved (NS up to 0.76 for THg and 0.85 for MeHg) by adding two to four parameters to represent seasonality in riparian soil water THg and MeHg concentrations profiles. These results are consistent with the hypothesis that riparian flow-pathways and seasonality in riparian soil concentrations are the major controls on temporal variation of THg and MeHg concentrations in low-order streams.
    Keywords: Models, Theoretical ; Seasons ; Mercury -- Analysis ; Methylmercury Compounds -- Analysis ; Rivers -- Chemistry
    ISSN: 0013936X
    E-ISSN: 1520-5851
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